1. Field of the Invention
The present invention is directed to a holographic system for recording two separate holograms of a body surface of a patient with the holograms being spaced apart by a time interval so that movement of the body surface can be determined.
2. Prior Art
In phono cardiography, it is obvious to detect movement of the body surface, which movement is caused by the heartbeat, with the aid of microphones or a plurality of microphones. To detect this movement, it is possible to move the microphones between different points of measurement and to compare the signals which are received. However, such a method of determining body movement is based on the assumption that the signals are stationary. In addition, a number of microphones can be adjacently applied on the body surface. However, the latter will effect the movement by virtue of their weight and the spatial resolution is greatly restricted by virtue of their size.
In an article from Medical Research Engineering, June 1970, pages 5-7, a system for photographically determining a movement of a body surface of a patient is disclosed. In this system, a portion of light from a laser is directed on the patient's surface to produce an object wave and another portion of the laser beam is utilized as a reference wave with the reference and object waves being recorded to form a holographic recording of the body surface of the patient. To detect the image of the movement, the same film is exposed twice in succession by recording a hologram each time the laser is pulsed. Thus, two superimposed images or holograms are recorded on the film. If the subject moves between the two light flashes of the laser, a pattern will result on the film, which after development and upon illumination with coherent light such as a reference wave, will contain in addition to an image of the subject, interference fringes which enable interpretation of the movement of the body surface. The installation or system described in this article was intended for detecting respiratory movement of the human body. The laser, which functions as a light source, was turned on or actuated manually. However, a manual actuation of the laser permits only a very rough determination of the photographic time intervals and is at best applicable for the purpose for detecting a respiratory movement.